Wash the cucumber and slice it thinly into about 10 strips using a peeler.

Soak the cucumber slices in saltwater (500ml water with 1-2 tbsp coarse salt) for 5-10 minutes.

Shred the crab sticks and mix them with 1 tbsp minced onion, 2 tbsp mayonnaise, and 1 tbsp mustard sauce.

Prepare sushi vinegar by mixing 1 tbsp vinegar, 1 tbsp sugar, 1 tbsp water, and 1/2 tbsp salt.

Mix 250g cooked rice with the sushi vinegar and let it cool to room temperature.

Rinse the cucumber slices under running water and gently press to remove excess moisture.

Divide the rice into 10 portions and shape each into a small round ball.

Wrap each rice ball with a cucumber slice, ensuring it is tightly secured.